I have a S&W M&P15 that has the regular foreguard on it. So no rails, just the bayonet lug. Can anyone recommend a good way to mount a light to the front of the rifle. I have rails on the upper receiver, just not the foreguard.

I too have a std Sport 2 (and am new to AR’s), i believe a rail can be attached to the stock handguard if I understood some vids correctly.
I do know there are offset rail mounts available as well, though I cant say if using them on the one rail we do have would be too close to the ejection port or not.

The best way to do this is to purchase a Magpul handguard, IMO. Instead of buying pieces of rail, purchase a handguard that has heat shields as well as allows for attaching gadgets. I say Magpul because they are fairly inexpensive.

You have options like the included link, other rail adapters, etc.

MARSV2 Picatinny Rail for AR15 M4 Plastic Handguard - AR-15 Parts - AR-15 Accessories

I bought one of these:

Midwest Industries Tactical Light Mount AR-15 Aluminum Matte

Very solid & well built.

Mag-Pul has short rail sections that can bolt into the vent holes of the stock hand guard or you could drill a couple extras. They were made to fit the various Mag-Pul hand guards.

Various outfits, including G,G &G, make scope ring like mounts for various lights that attach to rails. Other lights, like the Streamlight TLR series, will mount directly to the rail.