You can serve this steak on slices of lightly toasted ciabatta rubbed with garlic.
Use a large, sharp knife to butterfly skirt steak (or have butcher do it) and cut into 4 portions. Combine paprika, cumin, 1/2 teaspoon salt and pepper and rub onto outer side (not cut side) of steak. Place spiced-side down on a platter. Set aside.
Preheat grill or grill pan to very hot. Meanwhile, heat oil in a skillet. Add garlic, onion, jalapeños and a dusting of salt and sauté over medium-low heat until soft. Add bell peppers, increase heat to medium-high and sauté until bell peppers just begin to wilt but are still slightly crisp, about 5 minutes. Remove pan from heat.
Place steak spiced-side down on grill or in pan and sear, close to source of heat, 2 to 3 minutes, until just starting to brown around edges but still nearly raw on top. Transfer to a serving platter, seared-side down. Briefly reheat peppers, add vinegar and basil, stir, then pour over steak, spreading to cover meat. Serve.