This page of the guide to Dragon Ball Z: Kakarot has a walkthrough for the Tough Break for Turtle side quest.
Time frame: From Evil Emperor Frieza - Episode 1: Bulma's Advice - Episode 1: Interplanetary Preps
Reward: 7,104 EXP, D Medal, Rice, Bean Paste, Fatty Giant Fish Steak, Meaty River Snail.
Where to start: South-Eastern Islands, as Gohan.
The turtle is waiting for you in the house. Talk talk to him to get this sub story.
Your task is to get 6 eggs, 7 rice and 1 Royal Tomato. Eggs can be taken from chickens or they can be bought. You get the rice from a mission or you can buy it from the merchant.
However, to get a Royal Tomato, you need to go to the farmer. He is in Yamcha's Hideout, near the barn with the red roof.
To get the tomato, you need to bring the farmer 10 energetic fish. They swim in a nearby river. Your task is just to jump into the water and get the fish.
Once you have all the ingredients, go back the Turtle to complete the mission.