1. Preheat oven 375f. Dice 1 large yellow onion and 2 small red bell peppers and mince garlic cloves.
2. Heat olive oil over medium-high heat - use a large pan or pot. Add the onion and bell peppers, and season. Cook until the onion is translucent and the peppers are just tender. Add garlic and cook, stirring often, until fragrant and now transfer into a 9x13-inch baking dish.
3. Return the pot to high heat and add your ground beef + season with the salt. Let cook. Meanwhile, add tomato sauce, ketchup, apple cider vinegar, packed light brown sugar, and Worcestershire sauce in a medium bowl. Add the tomato sauce mixture and stir to combine. Reduce the heat to medium-high and bring to a simmer, stirring frequently. Let thicken for about 5 minutes.
4. Transfer into the baking dish and stir to combine with the onions and peppers. Sprinkle the cheese evenly and arrange 12 slider buns or dinner rolls on top of the sloppy joe mixture in a single layer.
5. Lather butter on top of each bun and then sprinkle poppy seeds. Pop into the oven for about 10-15 minutes - remove and enjoy!
