Soak sushi rice in water for 45–60 minutes, then drain and cook in a saucepan with fresh water and a pinch of salt over medium heat for 10–12 minutes. Set aside to cool.

Boil water in a large pot and blanch napa cabbage leaves for 2–3 minutes. Transfer to a bowl of cold water to stop cooking and set aside to drain.

Heat 2 tablespoons of oil in a large skillet over medium heat. Add diced onion, minced ginger, and garlic, and sauté for about 2 minutes. Add grated carrot, bell peppers, and chopped mushrooms, cooking for another 3–4 minutes. Drizzle with tamari and season with spices, cooking another 1–2 minutes.

In a large bowl, combine the cooked rice with the sautéed vegetable mixture. Adjust seasoning if necessary.

Lay one cabbage leaf flat, place about 1.5–2 tablespoons of filling in the center, fold sides, and roll tightly. Repeat with remaining filling.

Add more oil to the skillet and heat over medium-high. Sear rolls seam-side down for 3–4 minutes each side until golden brown.

In a small saucepan, heat 2 tablespoons of oil over medium heat, add minced ginger and garlic, and sauté for 1-2 minutes. Stir in tamari, rice vinegar, and maple syrup. Mix cornstarch with water and add to sauce until thickened, about 3–5 minutes.

Transfer the golden-brown cabbage rolls to a serving platter, drizzle with warm brown garlic sauce, and sprinkle with toasted sesame seeds. Serve immediately.