Bring 1 1/2 cups stock and butter to a boil. Stir in rice and cover, reducing heat to a simmer.
In a food processor, process 1/4 cup stock, spinach, cilantro, jalapeo or serrano and scallions into a thick paste. Scrape into a bowl, rinse out processor bowl and return it to the base.
Combine ancho and remaining 1 1/4 cups stock in small pot and bring to a boil. Reduce heat to low and simmer to soften the pepper. When soft, process pepper and stock with fire-roasted tomatoes. Place tomato paste in the pot the ancho and stock were cooked in and stir 30 seconds over medium heat. Stir in the ancho-tomato sauce, season with pepper simmer and thicken 12-15 minutes.
Meanwhile, heat a cast-iron skillet over medium high heat and preheat oven to 300F. Combine chili powder, cocoa powder and cinnamon in a small bowl. Season chicken or beef with salt and pepper then rub mole spice blend into meat. Add oil to pan and wipe it around the entire pan. Add meat and cook 12 minutes for chicken and 8-9 minutes for flat-iron steaks, turning once halfway through.
Wrap tortillas in foil and place in oven to warm through.
Add reserved spinach mixture to rice, stir to combine. Cover pot and cook 2-3 minutes more. Turn off heat, let stand 5 minutes.
Remove meat to cutting board. Let meat rest under loose foil tent and add another tablespoon oil to skillet. Add onions and peppers, and season with salt and pepper. Cook onions and peppers 7-8 minutes to soften, then place on a serving platter or divide among dinner plates. Slice meat and add to platter or plate alongside onions and peppers. Place the giardiniera in small bowl as well as the ancho-tomato sauce. Arrange the slices of avocado on a plate and dress with lime juice.
Fluff green rice with fork, place in serving dish. To make tacos, pile sliced meat in flour tortillas and top with a little ancho-tomato sauce, some onions, peppers, hot relish and a slice or 2 of avocado. Serve with green rice alongside.