In a dutch oven, or similar, brown ground beef and break into small pieces with a wooden spoon or spatula.
Add the onion, garlic, bell pepper, and seasonings. Stir and cook until softened, about 5-7 minutes.
Add tomato sauce, beef stock, and pasta shells. Stir to incorporate then bring to a low simmer. Cover, stirring occasionally, cook until pasta is done.
Remove from heat and add Velveeta and stir to melt and incorporate. Season with salt, to taste.
