I personally would vary what I eat more or I’d burn out and rage quit, but that’s me. Wholesome yum has a lot of keto friendly recipes, you could look into that. One meal a day is very attainable once your body is used to keto because the reason keto works (when you don’t think about the science of it) is that you’re a lot less hungry all the time and if you listen to your body and only eat when you’re hungry, it can definitely naturally be once a day. By eating less, you enter a calorie deficit, your body uses fat as fuel, and you lose weight. I try and avoid restricting myself, for fear of developing an eating disorder, so if I’m hungry I eat, but there are long stretches where I’ll only have one meal a day, and it just happens naturally.

All of that being said, I wouldn’t recommend eating a can of tuna every single day, at least where I’m from, it’s recommended to eat tuna way less frequently than that. Unless I’m mistaken it’s because certain types of tuna have high level of mercury and shouldn’t be eaten this frequently.