How to stop under eating?

How do I not under eat if I eat until I’m full? I don’t eat a lot but I’m not trying to under eat.. i just eat until I feel full and stop. I wake up around 7:30 AM and at 8AM, I drink a 18oz smoothie that’s fruits, water and chia seeds. Sometimes I use almond milk or coconut water instead.

Around maybe 4-5PM I have something big, usually rice or pasta with steamed vegetables. Today I had like 2 cups plain pasta, steamed vegetables, a bit of cooked black beans and steamed mushrooms in soy sauce. (yes I eat stuff really plain, I feel sick if there’s too many sauces or spices)

And then at night usually around 9PM, I have another 8oz smoothie.

And then I sleep around 10-11PM.. sometimes 1-3AM if I’m not too sleepy.

I drink smoothies because it’s quicker, I don’t really like taking time to eat so I make smoothies and also because I can get in a lot of fruits because I don’t eat much of them.

And I am a vegan so that’s why I don’t mention having any meat or eggs or dairy.. I don’t have any eating disorder I just don’t eat as much as I should and people keep telling me they’re worried or ask if I’m starving myself but I’m not trying to