What type of insect is this and how can I prevent/treat them?

For me you have 3 options, as you are still in veg and the flowers won't be affected.... 1. Chemical warfare, treat the soil and plant with chemical based bug killer, you can get ones specific to aphids but this is only to be used in veg, not in flower. 2. if problem persists (into flower also) you can get predatory insects like ladybirds and similar for a relatively cheap cost. They demolish these types of insects. 3. Neem oil and insecticidel soap mixed with water and sprayed onto the plant is a proven method to make the plant un inhabitable for insects. You will also want to research how and why they've appeared so you can try to prevent it from happening again next time 🌱👍