Melt butter in olive oil in a heavy skillet over medium-high heat. When foaming subsides, add garlic and cook until fragrant. Add tomatoes and sauté for 2 minutes; add green beans and squash or zucchini; sprinkle lightly with Creole seasoning and lemon zest and toss to coat. Sauté until vegetables are just crisp-tender and remove to a platter, leaving pan juices behind; keep warm. Add spinach to pan and cook, turning, until spinach is wilted and coated with pan drippings; season with salt and pepper and remove to a bowl, drizzling with any remaining pan juices.

Wipe pan clean and add just enough olive oil to coat the pan; place over high heat. Blot fish dry with paper towels and sprinkle lightly with Creole seasoning; when oil shimmers and is almost smoking, working in batches if necessary, add fish to pan. Allow to cook, undisturbed, for 1 minute; shake pan until fish releases. Continue to cook until golden brown; turn and repeat, reducing heat if necessary to prevent burning.

To serve, divide spinach among 4 plates. Top with sautéed vegetables, then with fillets of fish. Garnish with lemon, lime, and parsley. Pass lemon wedges at the table.