Adjust rack to middle position and preheat oven to 425 degrees. Wash and dry all produce. Peel and dice sweet potatoes into 1/2-inch pieces. Halve, peel, and cut onion into 1/2-inch-thick wedges.

Toss sweet potatoes and onion on a baking sheet with a drizzle of olive oil and a pinch of salt and pepper. Roast on middle rack, tossing halfway through, until browned and tender, 25-30 minutes.

Meanwhile, halve tomatoes. Finely chop cilantro leaves and stems; place 1 TBSP (2 TBSP for 4 servings) in a large bowl and set aside. Mince garlic. Halve lemon. Halve, pit, peel, and dice avocado. Mince chili.

In a small bowl, combine remaining cilantro, half the cumin (all for 4 servings), a pinch of garlic, and a pinch of chili to taste. Stir in a squeeze of lemon juice and a large drizzle of olive oil. Season with salt, pepper, and more garlic and chili if desired. TIP: Add more lemon juice and olive oil as needed until mixture reaches a drizzling consistency.

Cut half the grilling cheese (all the grilling cheese for 4 servings) into 1/3-inch-thick slices. When sweet potatoes and onion are almost done, heat a drizzle of olive oil in a large, preferably nonstick, pan over mediumhigh heat. Add grilling cheese and cook until browned, 1-2 minutes per side.

To bowl with reserved cilantro, add tomatoes, sweet potatoes, onion, avocado, a squeeze of lemon juice, and a pinch of remaining chili to taste; toss to combine. Divide between plates and top with grilling cheese. Drizzle with chimichurri and serve.