Adjust rack to top position and preheat oven to 450 degrees. Wash and dry all produce. Cut sweet potatoes into 1/2-inch-thick wedges. Trim and peel onions, then cut into 1/2-inch-thick rings, keeping them intact. Mince a few slices until you have 2 TBSP. Drain pineapple; discard any juice.

Toss sweet potatoes on a baking sheet with a large drizzle of oil, pepper, and a large pinch of salt. Roast, flipping halfway through, until browned and tender, 20-25 minutes. Meanwhile, in a small bowl, combine mayonnaise and sriracha (to taste).

In a large bowl, combine beef, minced onion, 2 TBSP teriyaki sauce (you’ll use the rest later), pepper, and a couple large pinches of salt. Form into four equal-sized patties, each slightly wider than a burger bun.

Heat a drizzle of oil in a large pan over medium-high heat (use a nonstick pan if you have one). Add pineapple and cook, stirring occasionally, until caramelized, 3-5 minutes. Transfer to a cutting board and roughly chop. Wipe out pan. Heat another drizzle of oil in same pan over medium-high heat. Add onion slices and season with salt. Cook until softened and charred, 3-4 minutes per side. Transfer to a plate.

Heat a drizzle of oil in same pan over medium-high heat. Add patties and cook until just shy of desired doneness, 3-5 minutes per side. Transfer to a plate. Wipe out pan and return to medium-high heat. Pour in remaining teriyaki sauce and simmer until thickened, about 2 minutes. Return patties to pan, turning to coat in glaze. Cook to desired doneness, about 1 minute more.

Halve buns. (TIP: If desired, toast buns until golden, 3-4 minutes.) Fill with glazed patties, pineapple, and onion slices. Serve sweet potato wedges and sriracha mayo on the side.