My husband was in the hospital recently for colon cancer surgery. I kept all his 'menu' sheets to help give me an idea about what to feed him when he came home. We never did get to meet with a dietician, so I used google, his menus, and how he felt as guidelines. I try to make everything taste good, and if that means butter, cream, cheese -- all the better.
Today, I made butternut squash (plus a couple of carrots) soup, roasting the veg, finishing with homemade chicken broth, and whizzing with the immersion blender. The broth came from poaching chicken breasts, which could be minced/pureed in a soup with rice. I've made tomato soup from fresh, roasted tomatoes - plus a couple of carrots to reduce the acidity and add a bit more fibre.
Think about soups, purees, creamy mashed potatoes. Soft fish quenelles. Yogurt with pureed fruit. Custards, either savory or sweet, should be ok, too. The hospital gave him all sorts of pureed veg, from cauliflower to broccoli and green beans. And yes, the hospital also gave him meal supplements, too - a couple of high-calorie boosts/day.