Making the green chile ketchup. Preheat the broiler. Roast the unpeeled garlic cloves, fresh green chiles and poblano chile under the broiler, turning once, until soft and blackened in places—6 to 8 minutes for the serrano and poblano chiles, 10 minutes for the garlic. Let cool, peel the garlic cloves and chop everything.
In a medium saucepan set over medium heat, combine the tomato paste, agave syrup, vinegar, roasted garlic, green chile and ¾ cup of water. Heat to a simmer, stirring regularly so the ingredients don’t stick to the bottom of the pan, and cook until the mixture reduces and thickens enough to hold it’s shape in a spoon—4 to 5 minutes. Cool completely. Taste and season with salt, usually ¾ teaspoon.
Finishing the cocktail. In a medium mixing bowl, stir together the cooled ketchup, cilantro, lime juice, chopped red onion, poblano chile and clam juice or water. Add the seafood and mix thoroughly. Gently stir in the diced avocado. Spoon the finished seafood cocktail into high ball glasses or small bowls and serve you’re your favorite crackers or tortilla chips.