Combine tequila, olive oil, lemon juice, mustard, chopped basil, and pepper and pour over the shrimps in a shallow bowl to cover them. Marinade in the refrigerator for a couple of hours. If the marinated does not cover them fully, turn the shrimps once.
On the stove heat up a grilling plate over high heat.
Remove the shrimps from the marinade and reserve the marinade. Wrap the middle of each shrimp first with a leave of basil and then with the prosciutto. Thread 4 shrimps lengthwise on each of 6 metal skewers. (if no metal is on hand, use bamboo skewers that you will have submerged in water for a couple of hours so they will not burn when grilling).
Grill the shrimps basting with the marinade for several minutes on each side. Serve immediately.