Preheat a gas or charcoal grill to medium-high heat and lightly oil the grates.
Pat the shrimp dry and season with ranch seasoning, salt, and pepper.
Thread about four shrimp onto each skewer.
Grill for 2–3 minutes per side until the shrimp become opaque and reach an internal temperature of 145°F (63°C).
Remove the shrimp from the skewers.
Divide the chopped romaine lettuce evenly among four serving bowls.
Add cooked brown rice to each bowl.
Arrange the grilled shrimp, sliced avocado, and corn over the rice.
Drizzle generously with cilantro lime ranch dressing.
Garnish with sliced green onions if desired and serve immediately.