Heat the olive oil in a medium pot over medium-high heat. Add the onions and cook until just beginning to get translucent, about 2 to 3 minutes.
Stir in the Serrano, tomatoes, and garlic. Cook until the vegetables are soft and fragrant, about 10 minutes, stirring often.
Add in the cumin, cilantro, lime juice, and salt and pepper to taste. Stir to combine. Cook about 10 minutes more, stirring often. Depending on how juicy your tomatoes are, you may need to add a little bit of water to the pan to prevent burning. Cool slightly before serving.
Begin heating a pot of vegetable oil over a medium flame up to between 350F and 360F.
Cut the plantains in ½-inch rounds. Before smashing the plantains you will need to par-fry them. Place the unsmashed rounds in the hot oil for 20 to 30 seconds. This will soften up the hard plantain for easy smashing. Using a tortilla press, or something similar, press your plantains until they are fairly flat disks. (I find that pressing them between two pieces of wax paper that have been sprayed with non-stick cooking spray will allow you to move through this process quickly and cleanly.)
Add the plantains back to the oil, a few at a time, being careful not to overcrowd the pan or the temperature will drop too much to fry properly. Flip halfway through frying. Allow them to fry until the plantains have a nice golden color, 2 to 3 minutes.
Carefully remove the plantains from the hot oil and allow to drain on a paper towel. Sprinkle with salt and dust with cumin immediately.
To serve, simply top your patacónes, or fried plantains, with hogao and enjoy!