Prepare the Beans
Drain and rinse the beans, reserving the liquid.
Mash roughly half of one can of beans with a fork to create a creamy texture when cooked.
Sauté the Garlic and Chili Flakes
Heat the olive oil in a large skillet over medium-low heat.
Add the sliced garlic and chili flakes (if using) and sauté until fragrant and just golden, about 1–2 minutes.
Cook the Beans and Spinach
Add the whole beans, mashed beans, spinach, salt, and pepper to the skillet.
Turn the heat up to medium and cook, stirring, for about 3 minutes until the spinach is wilted and any released water has evaporated.
Adjust Consistency and Add Lemon Juice
Stir in 1 to 2 tablespoons of the reserved bean liquid (aquafaba) and the lemon juice. For a soupier texture, add up to 1/4 cup of aquafaba.
Cook for 1 more minute, stirring to combine the flavors.
Serve
Transfer to bowls, garnish with grated Parmesan cheese if desired, and serve immediately.