Make the spicy honeydew salsa: In a sealable plastic bag, combine the honeydew and Sriracha. Press all of the air out of the bag, seal it and massage the sriracha and honeydew until all the fruit is coated, then refrigerate overnight.
The next day, in a large bowl, combine the marinated honeydew with the cilantro, lime juice, tomatoes, jalapeño and onion. Cover in plastic wrap and allow the mixture to marinate in the refrigerator until ready to serve.
Make the shrimp tacos: In a small bowl, combine 4 tablespoons of the olive oil and the smashed garlic, and let marinate for 30 minutes.
Light a grill, or alternatively heat a grill pan over medium-high heat. Grill the tortillas to warm through, 1 minute per side, then wrap in aluminum foil to keep warm. Pat the shrimp dry with paper towels, then brush them with the garlic oil. Thread the shrimp onto skewers and place on the grill. Cook, flipping once, until cooked through and lightly charred, 1 to 2 minutes per side. Transfer to a clean plate and remove the skewers.
Divide the tortillas between plates and top with the grilled shrimp. Garnish with the honeydew salsa and iceberg lettuce, then serve.