Toss the onion slices and peppers in olive oil and sprinkle with salt. Arrange the veggies in a grill basket and place on the cooler side of the grill over indirect heat, tossing occasionally until veggies are charred and softened,
7-10 minutes.
Arrange the patties on the hot side of the grill and close the lid. Grill 4-5 minutes per side until internal temperature reaches 160°F, flipping once halfway through for even cooking.