I prepared you a delicious ___.

The correct choice is "dessert." This word refers to a sweet course typically served at the end of a meal, such as cakes, pies, or ice cream, which aligns with the context of preparing something delicious.

In contrast, the spelling "dezert" and "dizert" do not correspond to any recognized English word and represent common phonetic misspellings. The word "desert" refers to a barren, dry area typically characterized by sand and sparse vegetation, which is unrelated to the context of preparing a meal. Thus, "dessert" is the only option that fits both the definition and the context of the sentence correctly.