Cut thighs into thin strips.
Heat oil in large skillet over medium heat.
Cook chicken, onions, peppers and tomatoes until chicken is no longer pink.
Sprinkle taco seasoning over mixture and stir to coat.
Continue cooking for 5 minutes.
Heat heavy skillet over medium heat.
Place a tortilla in skillet.
Top tortilla with meat and vegetable mixture and sprinkle cheese liberally over the op.
Place another tortilla on top.
Place a smaller skillet on top to gently press down.
Allow to cook for 2-3 minutes or until bottom is starting to brown.
Remove skillet and flip. Replace smaller skillet and cook for 2-3 more minutes or until that side is lightly browned.
Remove to another plate and cook remaining quesadillas in similar manner.