Coat a stove-top grill pan or griddle with cooking spray and preheat to medium-high. Season both sides of the mahi mahi with salt and pepper.

In a small bowl, combine the chili powder, cumin, marjoram, thyme, onion powder, garlic powder, cayenne pepper and 1 teaspoon of the grated lime zest (reserve the lime for its juice). Rub the mixture all over both sides of the mahi mahi. Place the mahi mahi on the hot pan and cook for 3 to 4 minutes per side, until the fish is opaque and fork-tender.

In a small bowl, combine the avocado and 1 tablespoon of the lime juice.

Cut the fish into bite-size pieces. Arrange the fish on the tortillas and top with the beans, avocado, tomatoes and cilantro.