Wash and dry all produce. Preheat a grill for direct heat. (TIP: If cooking indoors, heat a grill pan or large pan over medium-high heat). Zest 1 tsp zest from lime, then cut into quarters. Pat steak dry with a paper towel and season with plenty of salt and pepper.

Sprinkle steak all over with half the spice blend and half the lime zest. Squeeze juice from one lime quarter over steak, then rub seasonings into meat. Set aside to marinate.

Quarter bell pepper lengthwise through stem end, removing stem, ribs, and seeds. Peel onion, then cut into 1/4-inch-thick rounds. Mince jalapeño, removing ribs and seeds for less heat. In a small bowl, stir together sour cream, juice from another lime quarter, 2 TBSP water, and remaining spice blend and lime zest. Season with salt and pepper.

Brush grill grates with oil (or heat a drizzle of oil in your pan). Add steak and cook to desired doneness, 3-6 minutes per side (4-7 minutes per side in a pan). Set aside to rest on a cutting board or plate.

Brush bell pepper and onion with a drizzle of oil. Season all over with salt and pepper. Grill (or cook in pan) until softened and charred in spots, 4-5 minutes per side, flipping halfway through. Add tortillas to grill (or pan) and grill until warm and light grill marks are visible, 20-30 seconds per side.

Slice steak against the grain into thin strips. Cut bell pepper into thin strips. Separate onion into rings. Divide steak, bell pepper, and onion between tortillas. Drizzle with crema. Garnish with jalapeño if you like it spicy. Serve with remaining lime quarters for squeezing over.