Preheat oven to 350 degrees. In a very large skillet, over medium, heat some olive oil. Saute onion until translucent, about 8 minutes. Add cabbage and kale and saute until just wilted. Add thyme and mix with gruyere cheese. Melt butter and mix with Panko. Butter a baking dish, add cabbage/kale mixture and top with bread crumbs. Bake for 30 minutes.