Pre-cook potatoes until softened, but not fully cooked (about six minutes in the microwave will do it for smaller potatoes; adjust as necessary for larger ones or boil until slightly tender). Let potatoes cool, then chop them.
Heat olive oil in a large skillet over medium heat until shimmering, then add onion and saute for two minutes.
Stir in potatoes, garlic, and spices, and saute another seven minutes, stirring occasionally, until potatoes are browned.
Add bell pepper, chopped chipotle pepper, and sauce and continue cooking over medium heat for another three minutes.
Stir in beans and spinach, then continue sauteing, stirring occasionally, until spinach is wilted and beans are heated through.
These tacos would also be great with sweet potatoes rather than russet; I just had the end of a bag of those to use up today.