Preheat oven to 375° degrees.
Take the sweet peppers, and with a small knife or paring knife, cut about a third of the way through the pepper lengthwise, leaving the stem intact (see photo). Keep the pieces cut off and finely chop them and set aside with the chopped onions. Scoop out any seeds from the sweet peppers.
Heat a large sauté pan over medium heat and add the oil. When the oil is hot, add the chopped onions and sweet peppers and stir to combine. Let sauté for about 3 minutes or until they start to soften. Add the garlic, cook for another minute, then add in the ground beef, breaking it up in the pan with a spoon or spatula. Let the beef cook for about 8-10 minutes or until mostly cooked through, stirring occasionally. Stir in the sauce and reduce the heat a little. Let the mixture simmer until the beef is cooked through and the sauce has reduced a little, about 5-10 minutes. Let the mixture cool until it's cooled down enough to handle, then season to taste with salt and pepper.
Line a large baking sheet tray with aluminum foil. Using a small spoon, stuff each sweet pepper with the filling and place them on the baking tray. Bake for 10-15 minutes or until the peppers are soft and slightly wrinkly. Top with cheese and bake for another minute or two until the cheese melts.
Let the peppers cool until they can be handled, then place them on a serving tray and garnish with cilantro and a drizzle of Sweet Heat sauce. Serve immediately.