Preheat the oven to 425° fahrenheit.
Wash, scrub and dry the sweet potatoes. Then cut slits across them. They should be about 1/8 of an inch apart (roughly - you don't have to be too meticulous here) and 2/3 of the way down the potatoes.
Put the potatoes on a large pan lined with parchment paper. Coat them in about 1/4 cup (4 tbsp) of olive oil. Make sure that it gets into the cracks and crevices! Then sprinkle the tops of the potatoes with salt and freshly ground pepper (to taste).
Put the potatoes in the preheated oven for 60-75 minutes, or until tender (pierce the side of one of them with a fork to test this).
While the potatoes are in the oven, make the sauce. Put the garlic, jalapeño, cilantro, parsley, 1/4 tsp salt, and 1/4 tsp freshly ground black pepper in the base of your food processor or blender. Pulse a few times until everything is finely chopped. Don't let it go too long, otherwise you'll end up with a purée.
Add the lemon juice, white wine vinegar, and 1/4 cup olive oil to the food processor and pulse a few more times until everything is combined.
When the potatoes are ready, spoon some sauce onto each one. Sprinkle with a little bit of flaky sea salt (if using), and serve!