Cut the avocados in half lengthwise. Remove the pit from the avocado and throw it away. Scoop the avocado from the skin with a large spoon, and place the flesh of the avocado in a mixing bowl. Add the lime juice, red onion, cilantro, and salt into the mixing bowl. Using a fork begin mashing the avocado flesh and the other ingredients together until the mixture is completely combined. You are looking for a texture that is in between chunky and smooth. Serve with tortillas.