Add oil, ghee, or tallow to a pan at least 3 inches deep on medium heat. A deep cast-iron skillet works well.
When oil is hot, add sliced plantain and make sure they’re evenly dispersed in the oil and not overcrowding the pan. Fry until the outsides are a light golden and they are soft enough to pierce with a fork. If needed, work in batches to fry.
Remove slices and drain on paper towels. Using the bottom of a mason jar, squash and flatten the plantains until each one is about 1/4-inch thick.
Add slices back into the hot oil and fry until golden brown and crispy. Drain on fresh paper towels and season immediately with salt.
Prepare guacamole: Peel and pit your avocado, then mash with lime juice until the mixture is mostly smooth. Season to taste with salt.
Serve tostones with guacamole and garnish with fresh oregano leaves.
