Cut the avocados in half, remove the pit, and scoop the flesh out with a spoon. Place the avocado flesh in a medium bowl and pour the lime juice over the top. Use a spoon and fork to mash the avocado until mostly smooth.
Smell your jalapeño to test the heat... You can usually tell if you got a spicy one. Stir in the garlic, jalapeño (half or all), green onions and cilantro. Salt and pepper to taste. Stir in the diced tomato at the very end.
Serve immediately, or press plastic wrap down over the surface of the guacamole, removing all air bubbles, and refrigerate until ready to serve.