In a mortar, pound together the garlic and the parsley. In a bowl, season the meat with salt and pepper and add 1/2 of the garlic and parsley mixture. Mix well. Add 1 tablespoon of water. Continue mixing until a paste forms.

In a skillet, heat 1/4 cup olive oil on medium-high heat. Add 1/2 of the chopped onion and sauté until translucent. Add the meat mixture and cook at medium heat, stirring so the meat breaks up, until almost done. Mix in the bread crumbs. Transfer to a bowl.

Drain the piquillo peppers in a colander and reserve the liquid. In a small saucepan heat 1/4 cup olive oil at medium heat. Add the remaining chopped onion and cook until translucent. Add the remaining garlic and parsley mixture and cook for 2 minutes. Add the tomato and cook an extra 4 minutes. Add 1 tablespoon of the flour and mix well. Add the reserved liquid from the peppers and 1/4 cup of wine (if using) or water. Increase the heat to high and cook, stirring, for 4-5 minutes. Lower the heat to low and cook the sauce until it reduces a bit, about 10 minutes. Remove from the heat. Pass through a foodmill and reserve (you can also purée with an immersion blender).

Meanwhile, spread the remaining flour in a shallow bowl. Carefully fill each piquillo pepper with the meat mixture, using a spoon and watching to not to overfill the peppers, as their delicate flesh might break.

In a large skillet, heat 1/4 cup olive oil over high heat. Working in batches, coat each pepper with flour on all sides and add to the skillet with the hot oil, as many peppers as the skillet will hold, without crowding the peppers. Lower the heat to medium and cook on all sides, about 1 minute per side. Transfer the peppers to a plate with paper towels to drain. Fry the remaining peppers in the same way.

Transfer the first batch of peppers to a cazuela or oven dish and replace the paper towels on the plate before transferring the next batch of peppers from the skillet.

When all the peppers are lined in the cazuela, pour over the sauce. Place the cazuela over medium heat and heat through for another 5 minutes (alternatively, you can place the cazuela in the oven at 350ºF for about 10 minutes. Serve with crusty bread.