Preheat oven to 350 degrees F.
Prep the vegetables for taco filling. First dice bell pepper and onions into roughly 3/4 inch pieces. Then peel potatoes and cut into bite size pieces, roughly 1/2 inch x 3/4 inch chunks. (Prepping the potatoes after the bell pepper and onion helps to avoid browning of the cut potatoes.)
Grease a large sheet pan with spray oil.
Transfer the diced bell pepper, onions, and potatoes to the sheet pan. Add olive oil, garlic powder, chili powder, oregano, and salt. Toss well to thoroughly coat vegetables with oil and distribute the seasonings.
Put sheet pan in the oven and cook for 40 to 50 minutes until potatoes are tender and golden brown in spots. If you like, stir the potatoes a bit during final 5 - 10 minutes to promote even browning.
While potatoes are in the oven, prepare the poblano lime sour cream. Heat the poblano pepper in a dry skillet over medium-high heat about 3-4 minutes per side (for a total of about 12 to 15 minutes) until poblano is well blistered and charred all the way around.
Remove poblano from skillet and place in paper bag or covered bowl for 5 minutes to allow the heat to soften and loosen the skin. (Be mindful that poblano peppers have some heat so you may want to use gloves.) Use a paring knife to remove as much of the skin as possible. Then remove stem, slice open the poblano, and use paring knife to remove seeds. Roughly chop poblano into pieces.
Transfer chopped poblano into small container suitable for immersion blending. Add sour cream, lime juice, cilantro, and salt. Use an immersion blender for several seconds to make a mostly smooth sauce. Taste and add more salt or lime juice as needed. Alternatively, you could use a small food processor to blend ingredients. Or do it by hand - finely chop the poblano and cilantro, then in a small bowl stir together with sour cream, lime juice, and salt.
Warm up corn tortillas if desired according to package instructions.
Serve the potato filling with tortillas and poblano lime sour cream. Assemble tacos and enjoy!
If you like, skip the poblano lime sour cream sauce and use your favorite taco toppings. Any combination of cheese, chopped tomatoes, salsa, hot sauce, or guacamole works well.