Combine the herbs or greens, nuts or seeds, garlic, cheese, lemon juice, and salt in a food processor. Pulse until everything is very finely chopped, scraping down the sides of the bowl as needed.
Pour the olive oil into the food processor, then puree until the pesto looks smooth and a bit creamy. If you like a looser pesto, add 1 or 2 more tablespoons of oil and process until smooth.
Taste the pesto and season as desired with more salt and/or lemon juice.
To store the pesto, transfer it to one or two airtight containers (this recipe makes enough for two 4-serving pasta meals). Press a piece of plastic wrap onto the surface of the pesto, then seal the container. Refrigerate the pesto for up to 1 week or freeze for up to 3 months.