Tunnel minded is kind of like closed minded. Except tunnel minded is like a one-way mind. Kind of like a tunnel. that goes one way. So Tunnel minded is an adjective which means a mind that only thinks in one direction and will not be changing the direction or open a new opening anytime soon.
"Hey Sam, what came first? The chicken or the egg?"
"I think the chicken. What about you Tommy?"
"I can't make a decision. I see both sides of the argument and I just can't think....."
"It has to be the chicken. Whoever says the egg is stupid."
"Don't be so tunnel minded, Sam!"