Heat grill to medium-high. Once it’s hot, clean the grill grate with a wire brush. Just before grilling, oil the grill grate.
Mash the garlic to a paste using the flat side of a chef’s knife. Combine with the olive oil, chili powder, cumin, oregano, ¾ teaspoon salt, and ½ teaspoon pepper in a medium bowl. Add the shrimp and toss to coat. Grill the shrimp until opaque throughout, 1 to 2 minutes per side. Grill the tortillas until pliable, about 30 seconds per side. Divide the shrimp among the tortillas and top with the Pineapple-Jalapeño Salsa.