Cook the Book: Herb Green Ceviche with Cucumber

Name: Cook the Book: Herb Green Ceviche with Cucumber
Ingredients: For a scant 1 cup of herb seasoning:; 1/2 head garlic, cloves broken apart, unpeeled; 2 to 3 fresh serrano chiles; 1 medium bunch cilantro (thick bottom stems cut off); 1 small bunch flat-leaf parsley (thick bottom stems cut off); 1/2 cup olive oil; Salt; For finishing the ceviche:; 1/4 cup lime juice; 1 1/2 pounds sashimi-quality skinless, boneless fish fillets; 2 (7 ounces total) small pickle cucumbers or Persian (baby) cucumbers, cut into 1/2-inch cubes; 2 ripe large avocados, pitted, flesh scooped from skin and then cut into cubes; Lettuce leaves (butter lettuce works great here), for garnish