Preheat oven to 350° F.

Spray a 9×13 dish with pan spray. Pour all 4 cans of beans into the dish and set aside.

In a medium sauté pan, heat oil over medium-low heat until shimmering. Add onions with a pinch of salt and cook over low heat, stirring occasionally, until onions are very soft, about 10 minutes. Add garlic and cook for a few more minutes.

Remove from heat.

Add vinegar, sugar, dry mustard, tomato paste and black pepper to cooked onions and mix.

Carefully pour mixture over beans. Gently stir until well combined.

Bake for 40-50 minutes until beans are bubbly around the edges.