Preheat oven to 375F and heat grill to medium-high.
Place pineapple rings on the grill until they have char marks, around 2-4 minutes, turning once. Chop and reserve for relish.
For the relish, heat a saucepan over medium heat. Add oil and saute onions, green peppers, fresno and garlic until soft, around five minutes. Add the grilled pineapple, cider vinegar, lime juice and zest, whole grain mustard and season with salt and pepper. Reduce uncovered for 30 minutes on low heat then transfer to a container and let cool. Once the relish is cooled, stir in cilantro.
Heat a nonstick or cast-iron griddle on medium heat. Parboil the hot dogs in simmering water to heat them through.
Place bacon on a slotted broiler pan and bake until crisp, around 15 minutes. Remove and cool the bacon to handle.
Place hot dogs on the grill until they have charred marks, around 2-4 minutes turning once.
Serve dogs on toasted rolls with bacon and pineapple relish.