In a slow cooker, combine the diced onion, minced garlic, and grated ginger. Add the chicken pieces on top.
In a separate bowl, whisk together the coconut milk, red curry paste, soy sauce, brown sugar, turmeric, cumin, salt, and black pepper. Pour this mixture over the chicken in the slow cooker.
Add the chicken broth and stir gently to combine all the ingredients.
Cover and cook on low for 6-8 hours or on high for 3-4 hours, until the chicken is tender and cooked through.
About 30 minutes before serving, stir in the frozen peas and sliced red bell pepper. Cover and continue to cook until the vegetables are heated through.
Serve the curry over cooked rice or quinoa and garnish with fresh cilantro.