Preheat oven to 375°F. Line a baking sheet with parchment paper. Carefully lift the skin up from thigh end of a chicken leg. Divide and slide garlic slices underneath the skin, pushing them to different points around the leg. Set legs onbaking sheet.
Combine remaining ingredients in a small bowl, and then brush over the chicken. Roast legs, basting with pan juices occasionally, for 50 to 55 minutes, or until cooked through.
Heat oil in a wide pot set over medium, to medium-high heat. Add the onion, peppers and garlic and cook 4 to 5 minutes, until tender. Add tomatoes, stock, beans, tomato paste, cumin, chili powder, cayenne and sugar. Bring to a simmer for 10 minutes. Stir in chopped oregano, salt and pepper. Simmer 5 minutes more.
Divide beans among 4 shallow bowls. Set a chicken leg in each bowl. Garnish each bowl with a few oregano sprigs and lemon slices, and serve.