Sheet Pan Beef Fajitas

Name: Sheet Pan Beef Fajitas
Ingredients: 1½ lb. flank steak, sliced into thin strips; 1 lb. bag mini sweet peppers, cut in half lengthwise and seeded; 1 large red onion, thinly sliced; 2 T. extra virgin olive oil; 1 T. ground cumin; 2 t. chili powder; ½ t. cayenne pepper; 1 t. red pepper flakes; Sea salt and black pepper, to taste; ½ c. fresh cilantro leaves, roughly chopped; 1 large lime, sliced; Optional:; 1 large avocado, diced; Corn tortillas or large lettuce leaves