Heat a large cast-iron skillet over medium heat and drizzle in olive oil.
Add the merguez sausage and cook until browned on all sides, making sure it’s fully cooked (about 10 minutes). Remove and set aside on a cutting board to cool before slicing thinly.
Wipe out most of the grease from the skillet, but leave any browned bits for flavor. Add more olive oil to coat the bottom.
Sauté the celery, onion, and bell pepper over medium heat for about 10 minutes, stirring occasionally until softened and fragrant.
Add minced garlic and cook for another 1 minute, stirring frequently to avoid burning.
Stir in the black-eyed peas, corn, fava beans, lima beans, butter, kosher salt (2 teaspoons), and freshly ground black pepper (1 teaspoon). Cook until everything is fully heated through, about 10 minutes.
Return the sliced sausage to the skillet and mix it into the succotash, cooking another 2 minutes.
Remove from heat and gently add the cherry tomatoes, fresh lemon juice, zest, and chopped parsley. Serve warm.