There are tons of variations on succotash—a dish with Native American roots—but this skillet version explodes with summery flavor. Tomatoes, lemon juice, and basil add freshness, while the combo of lima beans and corn brings plenty of fiber.
Bring a small saucepan of water to a boil over high; add lima beans. Reduce heat to maintain a gentle boil and cook until tender, about 15 minutes for fresh and 8 to 10 minutes for frozen. Drain.
While beans cook, season grouper with 3/4 teaspoon salt and 1/4 teaspoon pepper. Melt 1 tablespoon butter with olive oil in a large nonstick skillet over medium-high. Cook grouper, turning over once, until golden brown, firm, and flaky, 4 to 5 minutes per side. Transfer to a plate using a slotted spatula; cover with aluminum foil to keep warm.
Add corn and shallot to drippings in skillet; cover and cook over medium-high, stirring occasionally, until tender, about 4 minutes. Stir in tomatoes and lima beans; cook uncovered, stirring often, until heated through, about 2 minutes. Remove from heat. Stir in basil, lemon juice, remaining tablespoon butter, remaining 1/4 teaspoon salt, and remaining 1/4 teaspoon pepper. Return grouper to skillet. Garnish with additional basil before serving.