Since you're in such close proximity to the decking, if you use any strong chemicals, you're likely going to cause a bit of a mess. I'd suggest you try some warm water with dishwashing detergent and agitate the area with a stiff bristle scrubbing brush. Unfortunately, due to bricks being porous, they've likely sucked the stain and oil into their surface. If so, this might be a case of needing to wait until the stain fades.
Give the soapy water a shot and let us know if it was successful. If it's not, then we can look to other solutions.