DO-AHEAD TIP – VEGETARIANS ONLY: Sort, rinse and soak tomorrow’s beans overnight.
Season pork with salt and pepper to taste.
Heat the olive oil in a large skillet over medium-high heat. Add pork loin and brown on all sides (you don’t need to cook it through, you just want it nicely browned on the outside); transfer to a slow cooker.
Add onion and jalapeno pepper to the skillet; sauté until onion is translucent. Add garlic and continue to cook for about 1 minute. Remove skillet from the heat; add orange juice and whisk up all of the browned bits from the bottom of the pan; pour liquid into the slow cooker along with the onion and jalapeno. Add chicken broth.
Cover and cook on LOW for 6 hours or until pork is fork-tender. Transfer to a serving platter and keep warm.
Skim any fat from the slow cooker juices then transfer to a small saucepan. Whisk in cornstarch and cook until thickened. Whisk in lemon juice and orange zest then remove from the heat.
Serve sauce over sliced pork; garnish with orange sections.