In a shallow dish or large resealable bag, combine the soy sauce, 2 tbsp olive oil, 2 tbsp lime juice, minced garlic, smoked paprika, and black pepper. Add the steak, ensuring it's fully coated. Marinate at room temperature for 15 minutes while you prep other ingredients, or refrigerate for up to 4 hours for deeper flavor.
Cook the rice according to package directions. While it cooks, preheat your grill (or grill pan) to medium-high heat (about 400-450°F). Brush the grates clean and oil them lightly to prevent sticking.
Brush the zucchini planks and corn (if using) with 1 tbsp olive oil and sprinkle with 1/4 tsp salt. Place on the hot grill. Cook the zucchini for 3-4 minutes per side until tender and marked. Grill the corn, turning occasionally, for 8-10 minutes until slightly charred. Remove to a plate. Once cool enough to handle, cut the corn kernels from the cob.
Remove the steak from the marinade, letting excess drip off. Place it on the hottest part of the grill. Cook for 4-6 minutes per side for medium-rare (130-135°F internal temperature), or to your desired doneness. Transfer to a cutting board, tent loosely with foil, and let rest for 5-10 minutes.
While the steak rests, make the sauce. In a small bowl, whisk together the sour cream (or Greek yogurt), 2 tbsp lime juice, minced garlic, cumin, and salt. Add water, one tablespoon at a time, until it reaches a drizzling consistency. Thinly slice the rested steak against the grain. Cut the grilled zucchini planks into bite-sized pieces.
Divide the cooked rice among four bowls. Top with sliced steak, grilled zucchini pieces, and grilled corn. Drizzle generously with the creamy lime sauce. Garnish with avocado slices and chopped cilantro. Serve immediately.