In a food processor, combine avocado, jalapeño, garlic, cilantro, salt and pepper to taste, water and lime juice; process until smooth. Transfer to a small serving bowl, cover and set aside.
In a large skillet, heat oil over medium-high heat. Add scallops, in small batches to avoid crowding, and cook, turning once, for 1 minute per side or until firm and opaque; add more oil as needed in between batches. Immediately arrange scallops on tortillas, dividing evenly. Top with cabbage mixture and avocado sauce.
Top scallops with this brightly flavored Cabbage Slaw for Tacos Tips:* After removing the scallops from the skillet, you can individually add each tortilla to the skillet for about 15 seconds to reheat them before assembling the tacos.* For a milder avocado sauce, remove some or all of the seeds from the jalapeño.