Do more of that thing every day. Do less web surfing and less rumination.
It's all about mental habituation.
Allow me to randomly speculate that in your mental world, reading some Intellectually Fascinating Article has an extremely high priority, whereas eating dinner is just some stupid thing your body demands, and so because of this configuration of like/dislike or attraction/aversion you tend to chow down whatever is easiest so you can get back to the Fascinating Article.
That habit becomes deeply learned by your neural networks, reinforced by daily training. Fortunately your species has evolved the mysterious capacity of thinking and willing, so you can in fact make decisions that are counterintuitive to your own neural training.
You may find that you need some violent tactics such as temporarily cutting off your internet supply. That snaps you back to reality (oh, there goes gravity). Makes it way easier to focus on prepping veggies.
Isn't part of the problem that electronic or thought-based stuff moves too fast, is infinitely elastic and offers too little real friction-based resistance? Which leads to a stagnation of patience with actual passing time and physical reality. So I suggest doing whatever requires and encourages patience. Cooking is a great example because if you try to do it as fast as possible you will burn your garlic and that can very effectively train your neurons to chill out and do one thing at a time.