Drain one 7-oz. can sliced pickled jalapeños, reserving 1 Tbsp. brine. Set aside separately.
Heat 1 Tbsp. vegetable oil in a medium skillet or Dutch oven over medium.
Add 1 medium green bell pepper, halved, ribs and seeds removed, cut into about ⅛" pieces, and 2 large garlic cloves, finely chopped; cook, stirring often, until fragrant and bell pepper is beginning to soften, 1–2 minutes.
Add 1 lb. ground beef, 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt, and ½ tsp. freshly ground black pepper; cook, stirring and breaking up meat with a wooden spoon, until beginning to brown, 3–4 minutes.
Add one 28-oz. can baked beans, 3 Tbsp. ketchup, 1 Tbsp. garlic powder, 1 Tbsp. yellow mustard, and reserved 1 Tbsp. pickled jalapeño brine; stir well to combine.
Simmer beans, stirring occasionally, until bubbling and thickened, about 5 minutes.
Transfer burger beans to a serving dish and top with reserved pickled jalapeños.
