Not sure which plan you are on.
There is the
Disney Dining Plan (DDP) that includes 1 Quick Service, 1 Table Service, and 1 snack credit per person per night. The TS credit includes an entree, dessert and standard non-alcoholic beverage at lunch and dinner. At breakfast there is no dessert component.
If you are on the Deluxe Dining Plan (DxDDP) you have 3 dining credits and 2 snack credits per person per night. The dining credits can be used at either table service or quick service venues. At TS restaurants it includes an appetizer, entree, dessert and standard non-alcoholic beverage at lunch and dinner.
The Boathouse is a signature restaurant so any meal will require 2 TS credits (or 2 DxDDP credits) per person whether you are there for lunch or dinner. Also any item listed "For 2" would require 2 diners' credits.
On the dining plan the entree includes everything that is listed in the description of the entree. Some of The Boathouse entrees include Grilled Asparagus so that would be part of the entree. However, farther down on the menu is a list of "Sides" with price points. These are not included on the dining plan and would have to be paid OOP if ordered.
You can search the Disney Dining Reviews forum to see if anyone has posted a review that answers your question about the dishes you are interested in or contact The Boathouse through their website.