Focusing on your question should help us get to the root of what you're really struggling with.
How can I avoid such long 'walls' of one-sided dialogue and make the
description more interesting for the reader?
Wall of Dialogue May Not Be A Problem
Most readers will pick up a novel and scan pages for white-space breaks and quote marks in an attempt to see how much dialogue happens in a book to determine if they want to read it. So, walls of dialogue probably are not really a problem.
Especially if you consider some great writing (along your same genre) like Robert B. Parker's Now & Then (amazon link) :
This is an excerpt of the very first page and it has a "wall of dialogue" but it is fantastic writing.
He came into my office carrying a thin briefcase under his left arm.
He was wearing a dark suit and a white shirt with a
red-and-blue-striped tie. His red hair was cut very short. He had a
thin, sharp face. He closed the door carefully behind him and turned
and gave me the hard eye.
“You Spenser?” he said.
“And proud of it,” I said.
He looked at me aggressively and didn't say anything.
I smiled pleasantly. “Are you being a wise guy?” he said.
“Only for a second,” I said. “What can I do for you?”
“I don't like this,” he said.
“Well,” I said. “It's a start.”
“I don't like funny either,” he said.
“Then we should do great,” I said.
“My name is Dennis Doherty,” he said.
“I love alliteration,” I said.
“There I go again,” I said.
“Listen pal. You don't want my business, just say so.”
“I don't want your business,” I said.
“Okay,” he said. He stood and walked toward my door. He opened it and
stopped and turned around. “I came on a little strong,” he said.
“I noticed that,” I said. “Lemme start over,” Doherty said.
I nodded. “Try not to frighten me,” I said.
He closed the door and came back and sat in one of the chairs in front
of my desk. He looked at me for a time. No aggression. Just taking
“You ever box,” he said.
I nodded. “The nose?” I said.
“More around the eyes,” Doherty said.
“Observant,” I said. “The nose has been broken,” Doherty said. “I can
see that. But it's not flattened.”
“I retired before it got flat,” I said. Doherty nodded. He looked at
the picture of Susan on my desk.
Let The Scene Play Out
Why not just let the scene play out? Just imagine the scene as it happens and provide the necessary details which hook the readers into what you (the author) understand to be important in the scene.
Try not to judge your writing from the viewpoint of
- Oh, that's too much dialogue
and instead, switch your requirement to
- Am I telling the story clearly enough that the reader can "see it
happen before her eyes"?
You can see in the excerpt, Parker gives a very brief intro and then lets the action play out in the interaction of the two characters in their dialogue.
That's what makes the scene feel real.
Let the characters interact and allow them to point out what seems to be important.
Be A News Reporter
Watch the scene play out in your mind. Then simply journal what you see the characters doing and saying. Just as if you are a news reporter. Allow the characters to talk and interact and then capture what they say and what they do.
Most importantly: Make sure they don't just say things to tell the reader. Make sure they interact with each other. Build tension. Make the detectives annoyed when your main character doesn't know or remember. Make the main character annoyed that they are pressing him so hard and making him seem like a liar. Out of that tension the story will build and the natural descriptions will arise.