Masking Bitterness is extremely difficult in many products.  The easiest ways are to add other tastes (e.g. sweet substances) that may cover up the flavor or to add flavors that tend to blend or overwhelm the bitterness (what these are totally depend on the application (e.g. garlic, onion might help in a sauce, vanilla in a beverage).  However, these change the overall flavor of the product.  Bitter masking agents are available commercially (do a search for companies that sell these), but they tend to be expensive.

I also wote for cyclodextrins plus another taste.

Masking of bitterness of powder is difficult task. In opinion before drying of moringa leaves carry out the blanching to inactivate enzyme and grind the dried leaves as low as temperature. Addition of other taste like sugar, salt will be carried before drying without affecting its quality.