Steak & Pepper Taco

1 pound flank or hanger steak Juice of 1 lime, plus lime wedges for serving 1 teaspoon kosher salt 2 garlic cloves, crushed 1/2 teaspoon mild chili powder 3 teaspoons vegetable oil 1/2 red onion, sliced 3 bell peppers, 1 each red, yellow, and orange, thinly sliced 1/2 cup fresh or frozen corn kernels 8 small corn tortillas, warmed 1/2 avocado, sliced 1/4 cup grated low-fat Monterey Jack 1/4 cup salsa verde or 2 tablespoons chopped fresh cilantro 2 tablespoons sliced pickled jalapenos Reduced-fat sour cream (optional)