You'll love the summer-y flavors in this Mexican-inspired grilled salad.
Prepare the grill for medium-high heat. In a bowl, whisk the mayo, sour cream, and lime zest and juice. Thin with 1 to 2 tbsp. water; season the crema with salt and pepper.
Cut the scallions to separate the light-green and dark-green parts. Leave the light greens in large pieces and slice the dark greens for garnish.
Brush the cabbage wedges, corn, and large scallion pieces with 3 tbsp. oil; season. Grill the corn and large scallion pieces, turning occasionally, until charred in spots, 5 minutes for the scallions and 10 minutes for the corn. Grill the cabbage until tender and charred in spots, 5 to 6 minutes per side.
In a medium bowl, toss the shrimp, cumin, and the remaining 4 tsp. oil. Grill until charred in spots, 1 to 2 minutes per side; season.
Cut the cores from the cabbage wedges. Chop the cabbage and the grilled scallions. Slice the kernels from the ears of corn. In a large bowl, toss the grilled veggies, cilantro, and half the crema. Top with the shrimp and avocado. Drizzle with more crema. Sprinkle with the sliced scallion greens.