Add the slivered almonds to a food processor and pulse on high until they are finely chopped. Then add the basil, mint, garlic, warm water, lemon zest and juice, salt, and pepper. Then, set the processor on continuous speed, and puree until creamy while streaming the olive oil in. If you like a slightly chunky pesto, skip the water and stop the machine before it becomes smooth.
Note: if you add the basil and mint at the very end instead of mixing it in with the rest of the ingredients, it's less likely to bruise or lose flavor. This will also help it maintain its bright green color.