По ошибке в той же печи одновременно находились баклажаны, перец и курица (курица была накрыта большую часть времени). Можно ли есть эти овощи вместе с рыбой (например, в качестве холодного салата)?

No, the vegetables should not be eaten together with fish in the same salad. Even though the chicken was covered most of the time while cooking in the oven, the vegetables absorbed some meat flavor from the oven environment. When foods cook together in an enclosed oven, there is zeah - steam and vapor - that transfers taste between the foods, even when one is covered. Since we have a prohibition against eating fish and meat together due to the health danger involved, and these vegetables now have meat status from cooking with the chicken, you cannot mix them with fish in a cold salad. The vegetables are considered fleishig (meat) and must be treated as such. If you want to eat these vegetables, you should eat them separately from fish. You could eat them with your meat meal, or eat them first, rinse your mouth with a drink and eat something solid to clean your palate, and then you could eat fish afterward - but not together in the same dish.