Season chicken with salt and pepper. Heat oil in a large pot over medium-high heat. Working in batches, brown chicken until golden. Transfer to a plate; discard fat. Add bacon; cook until crisp. Drain all but 1 tablespoon fat. Add onion, garlic, and couscous; cook until couscous is golden, about 5 minutes.
Add milk and thyme sprigs; bring to a simmer. Add chicken, skin side up. Reduce heat, cover, and simmer 30 minutes. Stir in corn and thyme leaves; cover and cook until liquid has almost evaporated, 15 to 20 minutes. Divide couscous and corn among 4 bowls. Top with chicken and arugula. Season with salt and pepper; drizzle with lemon juice and oil.
