"是什么"

Your sentence is fine except '食品', which is too formal I guess (as Minun has already mentioned). I think食品is more used in some food company's name. For example: ABC食品公司, other than食物公司. Such expression of 'my favourite 食品 is'....it makes sense of course, but it feels kind of odd. However, if I were you, I would say: 我最喜欢的食物是麻辣豆腐，它是一道非常好吃的素菜。 Besides, there is a more refined expression of 非常好吃, which is 美味可口. Your additional sentence: 我也喜欢红豆包子(maybe just红豆包,without子, it sounds nicer this way, but I'm not sure)，因为它很甜。

Avocado, it tast like egg but it is the fruit, healthy.

草莓，还有各种糕点。因为适合平时当零食吃，呵呵！ “你最喜爱的食品是什么？”有一个字错了，还有在日常使用中用“食物”会比“食品”更合适。另外通常大家不会这么问，而是问“你最喜欢吃什么？”

我最喜愛的食物是麻辣豆腐！因為非常好吃而且不含肉類！ （如果這個句子有問題請改正它） 青菜、水果、五榖雜糧！ 因為上了年紀, 飲食要崇尚自然！