Wash and trim the green beans, cutting them into bite-sized pieces. Dice the onions and slice the garlic thinly.

Heat 3 tablespoons of olive oil in a large pot over medium heat. Add the diced onions and sliced garlic, sautéing for about 5 minutes until fragrant and the onions become translucent.

Stir in the trimmed green beans and diced tomatoes, mixing well. Cover the pot and cook for about 5 minutes.

Pour in 40 ounces of tomato sauce, stirring to combine. Reduce heat to a gentle simmer and let cook for approximately 40 minutes, stirring occasionally.

Once the beans are tender, season with salt, red pepper flakes, and the lemon juice. Stir well and cook for an additional 5 minutes before serving.