Salsa rustica is an Italian-inspired blend of fresh herbs, capers, vinegar, and oil. Here, it's made with parsley and used to dress a sheet-pan supper of meaty sea-bass fillets, warm spinach, and garlicky sweet potatoes.
Preheat oven to 425 degrees. Toss sweet potatoes, garlic, and shallot with 2 tablespoons oil. Spread evenly on a rimmed baking sheet and season with salt and pepper. Roast until tender, 25 to 30 minutes.
Remove from oven. Drizzle spinach with oil and season with salt and pepper; scatter over sweet-potato mixture. Season fish with salt and pepper; place on top of spinach. Drizzle fish lightly with oil; roast until opaque and flaky, about 12 minutes. Stir together parsley, capers, remaining 3 tablespoons oil, and vinegar. Drizzle mixture over fish and vegetables; serve.
You can substitute basil or oregano for the parsley in the salsa rustica.