In a mixing bowl, mash ripe avocados until smooth, then fold in diced cilantro, jalapeño, red onion, and lime juice. Sprinkle with garlic powder, black pepper, and salt to taste. Cover with plastic wrap pressed directly on the surface and refrigerate until ready.

In a small bowl, combine crema or sour cream with minced chipotle peppers in adobo sauce and a splash of lime juice. Blend until smooth and creamy. Store covered in the refrigerator.

Preheat your grill to medium-high heat, around 400°F. Season both sides of the ribeye steak with salt and black pepper. Grill for 10-12 minutes until medium-rare, then let it rest for 5-10 minutes before slicing.

Toss shrimp in olive oil and Cajun seasoning. Skewer the shrimp and grill for 1-2 minutes per side until opaque and at 145°F. Remove and let cool slightly.

Spread guacamole over each tostada shell, layer on sliced grilled ribeye and shrimp, drizzle with chipotle cream, garnish with cilantro, and serve immediately.