Can I substitute powdered Harissa for the paste (or make a paste my whisking the powder with olive oil & water)?

I would use the exact same amount of powder, no oil required. A large batch of harissa only has a few tablespoons of oil, which isn't enough to make a difference. I've seen recipes call for both paste and powder interchangeably, not noting any measurement difference. Several recipes call for 1/2 tsp of powder exactly, just like this one.