What about where nuts are present as part of the meal, walnuts or pine nuts in a salad or pesto on pasta?
allnutritious.com/high-calorie-smoothie/
Bananas are good for snacks or you could slice one up to go on porridge or in pancakes.
Porridge is a good way to get high quality nutrient dense food in the morning, you could also make overnight oats.
Porridge with banana and maple syrup use whole milk, you could even add a drizzle of cream.
Apple pie or carrot cake porridge, grate an apple or carrot, squeeze out the juice and add the grated fruit/veg to the oats, add cinnamon/nutmeg/ginger whatever you like and a little brown sugar, milk and microwave for a minute at a time till it's the right consistency.
Overnight oats is just oats, full fat Greek yoghurt and whatever flavours you like, berries, syrup, spices. Leave overnight then give it a good stir and eat cold. Make it in a lidded jar and it's a good portable breakfast to take into work.
Eggs - omelette with mushrooms, peppers, onion, cold cuts or go spicy and have peppers, chilli and hot sauce. Add cheese to both. Or fried with sliced avocado on a nice seeded slice of toast or sourdough.