\begin{tikzpicture}
  \path[draw=lightGray, thick, shading=axis, top color=lightGray, bottom color=white]
    (0,0) --
      node[sloped, anchor=center, below]{%
        Estimate
      }
    (3,0) --
      node[sloped, anchor=center, above]{%
        Scope
      }
    (1.5, 2) --
      node[sloped, anchor=center, above]{%
        Importance
      }
    (0, 0);
\end{tikzpicture}