Pat 2pounds lean beef chuck cubed dry with paper towels. Place the beef in a bowl and toss with 2tablespoons flour until evenly coated.
Heat 1tablespoon canola oil in a large skillet over medium–high heat. When the oil is hot, add the beef (in batches if needed so it browns, not steams) and sear until browned on all sides, about 6–8 minutes per batch. Transfer the browned beef to your slow cooker.
Reduce the skillet heat to medium and add 1 onion minced and 1 to 2 jalapeño peppers minced. Cook, stirring occasionally, until the onion is softened, about 4–6 minutes.
Add 4 cloves garlic minced to the skillet and cook, stirring, for about 1 minute until fragrant. Transfer the onion/jalapeño/garlic mixture to the slow cooker with the beef.
Add 1tablespoon ground cumin, 1 chopped green chiles can drained, 3tablespoons ancho chili powder, 1teaspoon crushed red pepper flakes (more or less to taste), 1teaspoon dried oregano, 3cups beef stock fat-free and low-sodium, and 28ounces diced tomatoes with juice to the slow cooker. Stir everything to combine.
Cover and cook on LOW for 7–8 hours, until the beef is very tender and the chili is thick and rich.
Serve the chili topped with chopped green onions and fat-free Greek yogurt as desired.