Ingredients

• 1 

  large yellow onion (about 10 ounces)

• 2 

  small red bell peppers (about 6 ounces each)

• 6 

  large cloves garlic, minced

• 4 tablespoons 

  olive oil, divided

• 1 3/4 teaspoons 

  kosher salt, divided

• 2 1/2 pounds 

  lean ground beef

• 2 (15-ounce) cans 

  tomato sauce

• 3/4 cup 

  ketchup

• 2 tablespoons 

  apple cider vinegar

• 2 tablespoons 

  packed light brown sugar

• 2 teaspoons 

  prepared yellow mustard

• 2 teaspoons 

  Worcestershire sauce

• 8 to 12 ounces 

  shredded Mexican blend cheese (2 to 3 cups)

• 12 

  slider buns or soft dinner rolls

• 4 tablespoons 

  (1/2 stick) unsalted butter

• 1 tablespoons 

  poppy seeds

Description

1. Dice 1 large yellow onion (about 2 cups). Trim and finely chop 2 small red bell peppers (about 2 cups). Mince 6 large garlic cloves (about 3 tablespoons).

2. Arrange a rack in the middle of the oven and heat the oven to 375ºF. Heat 2 tablespoons olive oil in a Dutch oven or large pot over medium-high heat until shimmering. Add the onion and bell peppers, and season with 1/4 teaspoon of the kosher salt. Cook, stirring occasionally, until the onion is translucent and the peppers are just tender, about 7 minutes.