Add the olive oil, garlic, and chili flakes (if using) to a large skillet over medium-low heat.
Transfer about half of one of the cans of beans to a bowl and use a fork to roughly mash.
Once the garlic barely starts to turn golden and fragrant, add the beans (whole and mashed), spinach, salt, and pepper to the pan and turn the heat up to medium, stirring well to combine.
After about 3 minutes, the spinach should be relatively wilted and any water it released should have already reduced out.
Stir well, then add 1 to 2 tablespoons of the reserved bean liquid (aquafaba) and lemon juice.
Taste and season as needed before serving with freshly grated Parmesan cheese.
