Coat the slow cooker with cooking spray; layer the onion, bell peppers, and garlic in the cooker.
In a big skillet over med-high heat, warm 1 ½ tablespoon oil until very hot.
Add half the meat; cook until browned on all sides, 4-5 minutes; transfer meat to cooker.
Repeat with remaining oil and meat.
Add the tomatoes and wine to the skillet; bring to a boil, scraping up any browned bits stuck to the pan.
Add in the fennel, orange zest, rosemary, red pepper flakes, salt, and black pepper.
Pour over everything in the cooker; cover and cook on LOW for 7-9 hours, until pork is fork tender.
In a small bowl, whisk the flour and water together; whisk the slurry into the hot liquid in the slow cooker, increase heat to HIGH and cook, uncovered, for 15 minutes, until thickened; taste and add salt/pepper if needed.