Thirty minutes on Sunday buys four breakfasts. Squeeze the spinach dry before it goes in, or the muffins weep water and turn spongy.

Egg muffins solve the problem most high-protein breakfasts have, which is that they need cooking on the morning you are shortest of time. Three of these carry about 24g of protein, and they reheat in under a minute.
Eggs provide almost all of it. A breakfast built on protein keeps appetite quieter through the morning than one built on toast or cereal, and it barely moves blood sugar, which is why these carry all three goal tags rather than just one.
For women after menopause the protein matters for a less obvious reason. Muscle loss speeds up as oestrogen falls, and some research suggests spreading protein across the day, rather than loading it into dinner, supports muscle better; breakfast is the meal where most people fall shortest: losing weight in menopause. For men, the same muscle is part of the picture in foods that support testosterone.
Spinach adds folate and magnesium, and the red pepper brings vitamin C, which helps the body absorb the iron in both the spinach and the egg yolks.
A note on salt. Feta is one of the saltiest cheeses in the fridge, which is why the recipe adds none. Nearly all the salt in the batch comes from 100g of cheese, and that is enough.
If you would rather cook one fresh portion, the same flavours work as a spinach and feta omelette in eight minutes. More on the first meal of the day: breakfast mistakes that work against testosterone.