How to Make It
Heat oven to 350° F. Spread the pepitas on a rimmed baking sheet and toast in oven, tossing once, until fragrant, 6 to 8 minutes.
Heat grill to medium-high. In a medium bowl, toss the shrimp with the cayenne, 1 tablespoon of the oil, ½ teaspoon salt, and ¼ teaspoon black pepper. Grill until opaque throughout, 2 to 3 minutes per side.
In a large bowl, combine the vinegar, Worcestershire, jalapeño, garlic, the remaining 4 tablespoons of oil, and ¼ teaspoon each salt and black pepper. Add the lettuce, jicama, onion, pepitas, and shrimp and toss to combine. Sprinkle with the Cotija.