From the Bananas Wiki:
NPK of "Banana Peel: 0-3-42. Has a high percentage of Potash and no Nitrogen. An average store bought banana has a dried peel weight of about 8 grams, so the net amount of potash per peel is about 3 1/3 grams."
That's a lot of Potassium in a peel, but alone a pretty unbalanced fertilizer for Tomatoes. That's probably why composting them is a better idea.