Spinach and Chicken Tortilla Bake

extra-virgin olive oil4 chicken cutlets (about 1 pound)Salt and pepper1 1/2 cups store-bought salsa verde3/4 cup ricotta cheese4 large (8”³) flour tortillas1/2 red onion, thinly sliced3 cups baby spinach (about 1/4 pound)2 cups shredded pepper jack cheese