Short bouts of strength training - heavy weights for a few minutes 3 times a week.
Day 1: Arms, back, shoulders, stomach
Day 2: Legs, butt, etc..
Day 3: Cardio
Try Monday, Wednesday, Friday or some derivative thereof.
If you push your muscles enough, they will grow - but, make sure to eat high quality protein and carbs at about an hour after the workouts. The muscles will burn energy as they increase in size and your mitochondria multiply.
Eat small meals every 3 hours or so, few carbs to keep Sugar from dropping. Small meals will improve metabolism too.