Grenier's effort will be backed by Xtreme Drilling & Coil and NAPA.
"Mikael Grenier has done the bulk work of all the winter testing with the team," Moore said. "He is the best person to put us in a position for an excellent result in Long Beach. He has worked with his engineer and crew and is ready to go. So, at this time, we would like to give Mikael the opportunity to get back out there. He is a very deserving young man.
Grenier made five Firestone Indy Lights starts in 2011 – including a race with Team Moore Racing — posting a best finish of fifth at Barber Motorsports Park. He finished seventh in his only start on the streets of Long Beach.
"I would like to thank TMR/Xtreme Coil Drilling and all of my personal sponsors for this opportunity," the Canadian said. "I have to say it was really hard to be home watching the first two races on my computer rather than being in the car, especially after putting a lot of effort this winter in testing and developing the car together.
"Missing the first two races is not ideal, but I believe we are going to be very strong this weekend in Long Beach. I know the team and the people I will be working with very well and we just have to do our jobs like we always do and the result will come to us."