I will attempt this using my enameled dutch oven in my conventional oven.
I have never cooked leg of lamb as a traditional roast.  I am going to throw this stuff in with it.
Any idea?

Boneless leg of lamb

Rub with
Olive oil
garlic
rosemary
salt
pepper


Veggies:
onions
parsnips
carrots
potatoes
rutabaga
celery
?mushrooms? Maybe

I love me some lamb...

I would skip the routabaga, personally they can give off a bitterness. I would opt for fresh rosemary too.

Bone in or boneless? I prefer boneless stuff a bunch of whole garlic in the cavity and truss up the leg brown then slip in fresh rosemary twigs.

Mirepoix rack, hearty red wine and let it roast uncovered. Add veggies about midway. Until about 125-130*f pull it off the rack and let it sit, wrap in foil if you want. Drain juices into sauce pan, deglaze the and scrape the pan with red wine, dump in sauce pan with juices. Bring up to a simmer, skim, tighten with burre manie finish with mint jelly to taste. Fresh mint will leave a vegetal flavor so don't use it other than for garnish. The jelly will impart a nice mint background to the sauce which will be very complementary.

Add onions, but looks good.

D'oh!
Onions for sure

It looks like a good mix, though I would add onions (covered already) and either skip the mushrooms (my preference) or add them much later.

Roast lamb is tasty.

Also, I would be very generous with the garlic.  Maybe even stuff in some garlic cloves, inserted by poking a knifehole into the lamb.

I only make leg of lamb one way...

Butterfly
Marinade overnight in:

2:1 dry red wine/soy sauce
garlic
rosemary
mint
salt
pepper

Grill to rare/med rare

Mint sauce

Now when you say traditional roast...

We're talking this? Because I dont think all that stuff you listed will fit in the pan...

And dont forget the twine...