Add avocado, onion, jalapeño, lime, salt, cumin, and red pepper flake to a shallow mixing or serving bowl and mash with a fork or potato masher.
Add cilantro and stir. Then taste and adjust flavor as needed, adding more lime (or lemon) for acidity, cumin for smokiness, red pepper flake for spice, cilantro for herbal flavor, or salt to taste.
Serve immediately with chips or veggies of choice. Store leftovers well covered up to 2-3 days in the refrigerator, though best when fresh.
To extend freshness, squeeze a little more lime juice over the top of the guacamole (to prevent oxidation) before storing. And make sure a lid or plastic wrap is touching the surface of the guacamole (this also helps prevent oxidation). If the top appears slightly browned after storing, just scoop off the very top layer and the guacamole underneath is usually fine!
*2 small-medium avocados equal about 1 ½ cups small cubes lightly packed. *Nutrition information is a rough estimate for 7 (1/4-cup) servings (as the recipe is written).