Heat olive oil in a large skillet over medium-high heat until hot. Add sliced onions and cook for 4-5 minutes or until onions begin to brown and char. Add garlic and ginger; cook for an additional minute.
Transfer onion mixture to a slow cooker. Top with turmeric, cumin, salt, and cayenne pepper. Stir in butternut squash and tomato. Add vegetable broth.
Cover and cook on HIGH for 3 hours. Stir in fresh cilantro and garam masala. Gently mash the butternut squash and stir mixture until in thickens a bit.
Heat riced cauliflower according to package instructions.
Serve butternut squash mixture over riced cauliflower with a few squeezes of fresh lime.