Cook green beans in a medium pot filled with salted water: bring water to a boil, add beans, and cover and cook on medium-low until crisp-tender, about 5 minutes, depending on size.
Meanwhile, melt 1 tablespoon butter in a skillet over medium-low heat. Add chopped onions and cook, stirring occasionally, until caramelized, 5-8 minutes.
Add balsamic vinegar and cook a minute before adding the tomatoes, salt, pepper, and dried chili peppers. Cook another 1-3 minutes, and then remove from heat.
Drain the beans when they are done and toss with the remaining butter and more salt and pepper as you'd like.
Serving Options: 1)Place the beans on a serving plate and top with the onion-tomato mixture, OR 2) Toss it all together and serve in a bowl.
*My preference is drier paste tomatoes, but you can also use halved grape or cherry tomatoes, or chopped larger heirloom tomatoes (though squeeze juice and seeds from the halves before chopping).**Or olive oil for a dairy free version.Optional Variations:
Add fresh herbs (thyme, basil, or rosemary) at the same time as the tomatoes.
Add garlic at the end of caramelizing the onions.
Top the finished dish with crumbled or shredded cheese like feta, goat, or parmesan.