Meal replacement products exist, like Soylent or Ensure, protein powder shakes. There are various recipes for meal replacement bars but I wouldn’t vouch their healthfulness.
I make bulk soup as use it for one meal everyday throughout the weak.
I have a large list of calorie and nutrient dense foods I provide to weight gain clients that I can paste in if you’re interested, but I’m not sure it’s exactly what you’re looking for. Overall, variety is the easiest key to a healthful diet, but it sounds like meal prep might be an option for you if you’re really looking for speed - does that interest you?
Are you tied to keto?