Some great suggestions here, I might borrow some of these for my example menus for UA custom nutrition plans : ).
We are all (mostly) creatures of habit when it comes to breakfast, one of the key nutrients to include in breakfast (where most fall short) is protein. Then adding carbohydrate (in sufficient proportions in relation to you and your workouts) + some healthful fats and berries/greens.
Some example foods to include at breakfast:
Protein foods; tofu, eggs, dairy milk (almond, oat, rice milk are low in protein), cottage cheese, whey protein, vegan protein powder, greek yoghurt
Carbohydrates; Oats, fruit (berries, bananas), sour dough bread, muesli
Fats; lox, nuts, seeds, avocado
Greens/berries; kale, spinach, frozen berries can be a great to keep in the freezer
Breakfast ideas (in addition to the ones above):
Banana pancakes (my favourite) – 2 eggs, 1 x banana, whole oats (blended together into a batter), serve with toppings of choice e.g. yoghurt, berries, seeds, drizzle of maple syrup, honey as desired
Vegan banana pancakes (pre soak flaxseed in water as alternative to egg), banana, almond/spelt/oatmeal topped with nut butter (and any other toppings of choice)
Greek yoghurt berry and oat bowl (a good quality greek yoghurt is higher in protein) + muesli + berries + seeds
Scrambled tofu, avocado, spinach + add wholegrain toast/sour dough bread as desired/required
Fruit salad + Greek yoghurt, seeds
Smoked Lox, eggs, avocado, spinach, grilled tomatoes + grilled egg plant (aubergine)
Cottage cheese + lox (smoked salmon) on a wholegrain bagel with arugula (rocket), avocado
Cottage cheese + berries & seeds
Over night oats (in water, almond milk or milk) + topping of choice (berries/seeds/nuts/nut butter/dried fruit) + half a scoop of whey protein/vegan protein to make up protein intake.
Bircher muesli is another favourite of UA custom nutrition plan clients (can be prepped the night before)
Smoothies and protein shakes are also a great easy on the go breakfast (I would not worry too much about the sugar in the fruit, often we can add lots of ingredients to the smoothie and this can add to a significant amount of calories). I would suggest no more than 2 fruit options, can add oats, seeds, whey/vegan protein, any milk of preference, spinach, kale (lots of great recipes on line for smoothies).
Even a meal replacement shake can be a good option for ease at times e.g. Huel