Start by draining and rinsing the white beans in a colander until the water runs clear, then set them aside. Finely dice the yellow onion and mince the garlic cloves.

In a heavy-bottomed pot, heat 2 tablespoons of olive oil over medium-high heat until shimmering.

Add the diced onion to the pot and sauté for about 5 minutes until it turns soft and translucent. Stir in minced garlic, crushed red pepper flakes, salt, black pepper, and fresh herbs; cook for an additional minute.

Add the rinsed white beans, vegetable broth, and fire-roasted diced tomatoes into the pot. Stir gently to combine.

Bring to a rolling boil, then reduce heat to low and cover. Allow to simmer for about 25 minutes, stirring occasionally.

After 25 minutes, stir in lemon zest and taste the soup, adjusting seasoning as needed. Add chopped spinach or kale, if desired. Ladle into bowls and garnish with parsley or cheese.