Heat oven to 425°F. On a baking sheet, toss cauliflower and garlic together with ¼ cup olive oil, 2 teaspoons of salt, and ground pepper. Spread the mixture into an even layer.
Roast cauliflower in the oven for about 30 minutes, stirring once midway through, until the cauliflower is tender enough that you can squash it easily with a fork. Let it cool for a few minutes.
In a food processor, combine roasted cauliflower and garlic with peppers, lemon juice, pesto, and 2 teaspoons of salt. Blend to combine, scraping down sides with a spatula midway through, about 3 minutes.
Add the water and ¼ cup oil to the food processor, and blend for another couple of minutes until the mixture is smooth. Taste and adjust seasoning with additional salt, pepper, and lemon juice as needed.
Transfer the dip to a bowl and drizzle with olive oil. Serve with your favorite veggies, chips or bread. This dip may be covered and stored in the refrigerator for up to a week.