How quickly can metabolism be raised over time?

I'm basically eating at the maximum my body will handle — any more and I'd just get fat. My routine fits three meals a day with room to add a fourth at night. Without logging, here's what I usually eat. I want to figure out how to add that bedtime meal; if it means cutting rice or changing how I carb-load around workouts, fine. Breakfast: 3–4 eggs, 4 oz turkey, cheese, multigrain bagel or thick bread. I take whey isolate about two hours after breakfast. Lunch: 6–8 oz chicken, 1 cup white rice, 1/2 cup lentils. Whey isolate about two hours after lunch. Dinner: 6–8 oz chicken, 1 cup white rice, 1/2 cup lentils. Whey isolate about two hours after dinner. Post-dinner: 1.5–2 cups whole-milk cottage cheese with pineapple slices (this post-dinner meal sometimes doesn’t happen because my appetite is low — probably a sign I’m already eating plenty). I don't drink fruit juice or milk as drinks; mostly water, tea and black coffee. I usually don’t need pre-workout food unless it's leg day — typically a Clif Builders Bar before and after plus another big scoop of whey isolate. If I really need carbs for a session I’ll have two bananas with protein beforehand. I’m making gains and my main worry is getting enough quality protein for recovery. I’m trying to have just enough carbs to get by without going into a deficit.