Preheat the oven to 350°F.
Melt the butter in a medium-sized skillet over medium-low heat, add the onion, bell pepper, and garlic.
Cook until the softened and the onions are translucent, about 5-8 minutes.
Line a 9x13 baking pan with foil, spray with cooking spray, set aside.
While the onions and peppers are cooking, place the cheese, crackers, milk, ketchup, brown sugar, eggs, Worcestershire sauce, salt, and pepper in a large bowl and stir together until combined.
Add in the onions and peppers, stir to combine then add the ground beef to the bowl, I find using my clean hands to mix everything together is easiest.
Place the mixture into a 9x5 loaf pan to form it into an even loaf. Invert the pan and tap a few times on the bottom of the pan so the meatloaf will come out onto prepared baking sheet. If you have an issue getting it out of the pan, try running a butter knife along the edges. Alternatively, you can form a large loaf roughly 9x5 with your hands, but it may fall apart slightly while cooking.
Bake for 30 minutes.
While the meatloaf is baking, make the glaze by adding the ketchup, brown sugar, and mustard to a small bowl and stirring until combined.
After 30 minutes, glaze the meatloaf with the ketchup mixture then bake for an additional 20-30 minutes until the internal temperature reaches at least 165°F and the glaze has a baked-on appearance.
Let cool for about 10 minutes before slicing.