Not only is this loaded fork-and-knife entrée easy and cheesy, it's customizable, too. Make it your own with any produce or herbs you already have in your fridge. If you have the time, you could make your own pesto.
1 small red onion, peeled and cut into 1/4-in.-thick slices (about 8 slices)
1/3 cup prepared pesto
1 teaspoon olive oil
3/8 teaspoon kosher salt
1/4 teaspoon freshly ground black pepper
12 ounces shredded skinless, boneless rotisserie chicken breast
Heat a grill pan over medium-high heat. Coat pan with cooking spray. Arrange onion slices on pan; cook 2 minutes on each side or until lightly charred. Remove pan from heat; coarsely chop onions.
Combine chopped onions, pesto, oil, salt, pepper, and chicken in a medium bowl; toss well. Divide mixture evenly among mushrooms, pressing gently to fill each cap.
Return pan to medium-high. Coat with cooking spray. Gently transfer mushrooms to pan; cook 3 to 4 minutes or until mushrooms are heated through and tender. Sprinkle cheese evenly over chicken mixture. Transfer pan to oven; broil 2 minutes or until cheese melts and begins to brown.