Heat the olive oil in a large saucepan over medium heat until shimmering.

Add the minced onion and 1 teaspoon of salt and cook, stirring occasionally, until softened, about 5 minutes.

Add the minced garlic and cook until fragrant, about 30 seconds.

Stir in the crushed tomatoes with their juice, diced tomatoes, dried oregano, and red pepper flakes.

Bring the sauce to a simmer, then reduce heat to low and simmer until slightly thickened, about 15 minutes, stirring occasionally.

Season with salt and pepper to taste.

Use immediately in your lasagna or store for later use.