In a small glass bowl, whisk together the fresh lime juice, minced garlic, chili powder, cumin, sea salt, and black pepper until well combined.
Place the peeled and deveined shrimp in a shallow dish and pour half of the lime spice mixture over them, tossing to coat evenly.
Let the shrimp marinate for 10 minutes while you preheat a grill pan or outdoor grill to medium-high heat.
Lightly grease the grill surface and cook the shrimp for 2 to 3 minutes per side until they are pink, opaque, and have a light char.
Whisk the extra virgin olive oil into the remaining half of the lime spice mixture to create the zesty vinaigrette.
In a large serving bowl, combine the mixed greens, thinly sliced red onion, and diced cucumber.
Slice the avocado into thick wedges and arrange them over the greens along with the hot grilled shrimp.
Drizzle the prepared citrus vinaigrette over the entire salad and serve immediately while the shrimp is still warm.