Heat a grill to medium (350° to 400°). Toss onion rounds, jalapeño halves, and banana peppers with 1 tbsp. oil and 3/4 tsp. salt. Grill until tender and charred, 4 to 5 minutes per side.
Chop onions and transfer 1/4 cup to food processor (save the rest for topping). Add jalapeño, cilantro, garlic, lime juice, remaining 1/2 tsp. salt, and remaining 1 tbsp. oil. Process until smooth; set salsa aside.
Wrap each hot dog in a slice of bacon. Grill, turning occasionally, until bacon is crisp, about 12 minutes. Grill rolls, cut side down, until lightly toasted, about 30 seconds. Fill rolls with beans and hot dogs, then top with tomatoes, remaining grilled onions, mustard, and mayonnaise. Serve with grilled banana peppers and salsa.
*Find bolillo rolls in grocery stores in areas with large Latino communities or in Latino markets.